1. Field of the Invention
The present invention relates to a pentagonal roof reflecting mirror assembly for use in a viewfinder optical system of a single lens reflex camera and more particularly to a dust free modular unit that is capable of incorporating optical reflecting and refracting elements to compliment the viewfinder optics.
2. Description of the Prior Art
As is generally known, a pentagonal roof type reflecting mirror assembly is made up of a pair of roof reflecting mirrors and a third reflecting mirror to transmit an image of the object scene to a viewer for aiming and focusing the camera. With the advent of more sophisticated 35 millimeter cameras, there has been additional requirements of incorporating various information displays directly into the viewfinder screen to assist the viewer during photography.
A further requirement is the modern tendency to make the 35 millimeter camera as compact and light weight as possible. In this regard, there has been suggestions to utilize a plastic housing structure for the pentagonal roof reflecting mirror assembly. As can be appreciated by a skilled photographer, the pentagonal roof reflecting mirror assembly is removable on more expensive cameras in order to permit an optional changing of the focusing screens to accomodate a particular desired type of photography such as astro photography, dim light applications, dioptric and parallax focusing with close ups.
One suggestion to provide a lighter weight and economical plastic pentagonal roof reflecting mirror assembly can be seen in U.S. Pat. No. 3,603,200. Another example can be seen in U.S. Pat. No. 3,618,449 wherein side and rear wall members are provided to both reinforce the roof reflecting mirror and to prevent the introduction of undesirable or stray light. These plastic reflecting mirror assemblies are open at the bottom for coaction with the focusing screen and are subject to the entry of dust through the open bottom portion which will adhere to the mirror and effect the resulting image transmitted to a viewer. Additional prior art exists in the following;
Japanese Utility Model publication No. 47-24420, published on Aug. 2, 1972; Japanese Patent publication No. 47-4095, published on Feb. 4, 1972; Japanese Utility Model publication No. 47-20836, published on July 12, 1972; Japanese Utility Model publication No. 47-33315, published on Oct. 7, 1972; Japanese Utility Model publication No. 47-33317, published on Oct. 7, 1972; Japanese Utility Model publication No. 49-12602,, published on Mar. 28, 1974 and East German Pat. No. 50,419, published on Apr. 20, 1966.
There is a desire in the prior art to meet the demands of a compact 35 millimeter single lens reflex camera with an improved pentagonal roof reflecting mirror assembly that would be free from dust, economical to produce, and complimentary to both the viewfinder optics and the informational displays that are now required in viewfinder screens.